1. Field of the Invention
The invention relates to devices producing time varying acoustic pressures, and is directed more particularly to a flexible array of such devices adapted to conform to curved surfaces of underwater vehicles and thereby adapted to be mounted on such curved surfaces.
2. Description of the Prior Art
Flextensional transducers have been used as underwater transducers. Such devices have generally consisted of an active drive element and a shell structure, wherein the motion of the drive element produces a larger motion of the shell structure. Radiating surfaces of the shell structures typically are small compared to the generated acoustic wavelength, making the shell structures suitable for low frequency sonar applications.
In U.S. Pat. No. 5,276,657, there is shown and described an underwater transducer which includes a piezoelectric or electrostrictive ceramic disc with conductive electrodes bonded to its major surfaces. A pair of metal end caps include rims that are bonded to the conductive electrodes, respectively. Each end cap comprises a solid metal disc having a cavity formed in one major surface thereof.
In U.S. Pat. No. 5,729,077, a similar device employs sheet metal caps joined to opposed planar surfaces of the ceramic substrate. When the sheet metal caps are subjected to displacement by pressure, a resulting charge in voltage across the ceramic substrate is sensed. Because of the shape of the sheet metal caps, the transducer is referred to as a “cymbal” transducer. The '077 device has been employed as a hydrostatic sensor for underwater vehicles.
In U.S. Pat. No. 6,798,122, there is shown a compound electro-acoustic transducer for producing acoustic signals having a plurality of elements. Each element has a piezoelectric disk with electrically conductive plates fixed on the top and bottom sides of the piezoelectric disk. A stud is joined to an outer face of each plate. Conductors can be joined to each stud. The elements can be assembled on a resilient structure to form an array. Elements can be used in the array or individually accessed.
Many unmanned underwater vehicles (UUV) are provided with rounded hull surfaces. Because of the rigid nature of the hull surfaces and the rigidity of the arrays, the arrays do not readily conform to such surfaces.
There is thus a need for cymbal arrays which are sufficiently flexible to be mounted onto the curved hulls of underwater vehicles. It is further required that such arrays be sufficiently flexible to be conformed to surfaces exhibiting complex curves, such as bow or nose cone surfaces, which curve around the axis of the UUV and also curve from the outer portion of the hull to the axis of the hull at the center of the nose cone.